1. Field of the Invention
The present invention relates generally to a magnetic disk drive and a SCSI system employing the same. More particularly, the invention relates to a magnetic disk drive and a SCSI system employing the same, in which a plurality of hard disks are connected to an electronic equipment, such as a computer or the like with a SCSI (Small Computer System Interface).
2. Description of the Related Art
A hard disk drive (HDD) has been becoming an essential component of computers for large storage capacity. Because of easiness of enhancing data transfer speed of the HDD and easiness of extension, connection of HDDs according to SCSI standard has been used frequently.
In general, when a plurality of HDDs are connected on a SCSI bus for operation in multiplexed manner, if failure is caused in one of the HDDs, such faulty HDD may occupy the SCSI bus. In such case, other HDDs operating normally cannot transit to next sequence unless occupied condition of the SCSI bus by the faulty HDD is released. Therefore, if data exchange with one HDD cannot be terminated successfully or normally, a reset signal on the SCSI bus is forcedly made active from an initiator side, to release the faulty HDD from occupying state of the SCSI bus. In this case, what controls a bus phase of the SCSI bus is the HDD of target side, releasing of occupying of SCSI bus by the particular HDD is achieved only by making the reset signal on the SCSI bus active. However, according to SCSI protocol, if the reset signal on the SCSI bus is made active, all of the on-going processes for other HDDs connected on the SCSI bus are also cleared. Accordingly, in order to perform data transfer for the cleared HDDS, set values have to be re-set, again.
However, by the conventional SCSI controller, when the reset signal on the SCSI bus is forcedly made active from the initiator side, reset condition is caused in other HDDs connected to the SCSI bus. If this condition is caused, the setting established for exchanging data with the initiator becomes null to require re-establishment of the setting from the beginning.
On the other hand, the HDD in execution of SCSI command from the initiator side interrupts the process. As a result, for making the reset signal active, retry processes for respective HDDs associating with SCSI protocol occur for many times to require a long period for exchanging data.
Accordingly, it is an object of the present invention to provide a magnetic disk drive which permits control particular one of magnetic disk medium among a plurality of magnetic disk media on a SCSI bus and does not influence for other magnetic media, and a SCSI system employing the same.
According to the first aspect of the present invention, a magnetic disk drive performing exchange of data between a plurality of magnetic disk media and an external circuit through a common SCSI bus, comprises:
a plurality of reset control circuits respectively connected to the plurality of magnetic disk media by individual SCSI buses connected to the common SCSI bus, and responsive to an externally applied command data directed to own circuit, for making a reset signal on a reset signal line of the individual SCSI bus connected to the own circuit active.
With the construction set forth above, the reset control circuit parses the command data from the external circuit, such as a host. If the command data is directed to the own circuit, the reset signal on the reset signal line of the individual SCSI bus connecting the reset control circuit and the magnetic disk medium is made active. By this, sequence can be interrupted by causing the reset condition on the magnetic disk medium connected to the reset control circuit and process of other magnetic disk media connected to the reset control circuit and the common SCSI bus will never be interfered.
In the construction set forth above, it is preferred that the reset signal control circuit comprises:
a command data parsing portion parsing the command data to make judgment whether the command data in question is directed to own circuit or not; and
an execution processing portion making the reset signal on the reset signal line active for a given period when judgment is made that the command data is directed to own circuit as a result of parsing by the command data parsing portion.
According to the second aspect of the present invention, a SCSI system comprises:
a magnetic disk processing system serving as an initiator for performing exchange of data between a plurality of targets through a common SCSI bus; and
a plurality of reset control circuits respectively connected to the plurality of magnetic disk media as targets by individual SCSI buses connected to the common SCSI bus, and responsive to an externally applied command data directed to own circuit, for making a reset signal on a reset signal line of the individual SCSI bus connected to the own circuit active,
the reset control circuit making the reset signal on the reset signal line of the individual SCSI bus connected to the own circuit when the command data applied from the magnetic disk processing system is directed to the own circuit.
Similarly to the foregoing first aspect of the present invention, with the construction set forth above, the reset control circuit parses the command data from the external circuit, such as a host. If the command data is directed to the own circuit, the reset signal on the reset signal line of the individual SCSI bus connecting the reset control circuit and the magnetic disk medium is made active. By this, sequence can be interrupted by causing the reset condition on the magnetic disk medium connected to the reset control circuit and process of other magnetic disk media connected to the reset control circuit and the common SCSI bus will never be interfered.
Even in the foregoing constriction, it is preferred that the reset signal control circuit comprises:
a command data parsing portion parsing the command data to make judgment whether the command data in question is directed to own circuit or not; and
an execution processing portion making the reset signal on the reset signal line active for a given period when judgment is made that the command data is directed to own circuit as a result of parsing by the command data parsing portion.